1. Field of the Invention
The present invention relates to an electronic sphygmomanometer designed so that measured data which is stored in the memory can be transmitted to an external data processor by means of light communication.
2. Description of the Related Art
There has recently been proposed an electronic sphygmomanometer for finger which is provided with a pulse wave detecting photoelectric sensor designed to detect a pulse wave by a combination of light-emitting and -receiving elements.
FIG. 3 is a block diagram showing the pneumatic system and circuit configuration of the recently proposed electronic sphygmomanometer for finger.
A finger cuff 1 is defined by a cylindrical rubber bag formed such that a finger can be inserted thereinto. The finger cuff 1 has a pulse wave detecting photoelectric sensor 2 comprising a light-emitting element (light-emitting diode) 21 and a light-receiving element (phototransistor) 22 which are disposed on the inner peripheral surface of the cylindrical cuff 11. The finger cuff 11 is connected to a pressurizing motor 12 through a pneumatic tube 11. A slow exhaust valve 13, a rapid exhaust valve 14 and semi-conductor pressure sensor 15 are disposed at appropriate positions, respectively, along the pneumatic tube 11. The pressurizing motor 12 is connected to a motor driving circuit 31 which is, in turn, electrically connected to an MPU (microprocessor unit) 3 (described later), while the rapid exhaust valve 14 is connected to a rapid exhaust valve driving circuit 32, whereby the pneumatic system is driven and controlled. The semiconductor pressure sensor 15 detects the level of pressure inside the cuff 1 and outputs an analog quantity through an amplifier circuit 33. The analog quantity is converted into a digital quantity through an A/D converter 34 and this digital quantity is output to the MPU 3. It should be noted that another light-receiving element 16 for sensing a finger insertion condition is disposed at an appropriate position on the inner peripheral surface of the cuff 1.
The light-emitting element 21 of the cuff 1 projects light on the finger in response to an output command from the MPU 3, and the light-receiving element 22 detects the quantity of reflected light from the finger (i.e., the quantity of reflected light which varies in accordance with the change in volume of the artery). The quantity of reflected light is passed through a buffer amplifier 35 and the DC portion thereof is output to the MPU 3 through the A/D converter 34. The quantity of reflected light is also delivered to a filter 36 through the buffer amplifier 35. In the filter 36, the noise component (DC component) is removed and only a change in the pulse wave is taken out and amplified in an amplifier circuit 37. The amplified analog quantity is converted into a digital value in the A/D converter 34 and this digital value is output to the MPU 3.
The MPU 3 has a function of allowing the light-emitting element 21 to emit with an intensity appropriate to a subject of measurement through a D/A converter 38 and an LED driving circuit 39 and determining a highest blood pressure value and a lowest blood pressure value using a predetermined algorithm on the basis of the pulse wave amplitude of the pulse wave signal taken in from the light-receiving element 22 and the cuff pressure. The MPU 3 also has a function of storing the results of measurement (i.e., the determined blood pressure values) in a memory incorporated therein and digitally displaying the measured values on a display (LCD) 43.
To the MPU 3 are further electrically connected a power supply circuit 41 provided with a power supply switch 40 and a measurement start switch 42.
One type of the above-described electronic sphygmomanometer for finger is designed so that blood pressure values measured on a plurality of occasions, that is, past data, can be stored in the memory of the MPU for a predetermined period of time (e.g., one month). This measured data storage type electronic sphygmomanometer is considerably effective in diagnostically examining a change in the patient's condition since it is possible for an expert such as a doctor to make a diagnosis on the basis of a plurality of measured data (blood pressure values) obtained for a predetermined period of time which are transmittted from the electronic sphygmomanometer to an external special-purpose data processor (installed in a hospital or the like).
However, in order to transmit measured data obtained on a plurality of occasions and stored in the MPU (memory) from the conventional electronic sphygmomanometer to an external special-purpose data processor with a display unit which is installed in a hospital or the like, it is necessary to attach an interface to the MPU, connect together the instrument body and the special-purpose data processor through a connecting cable, and transmit measured data through this transmission line. Accordingly, there is a need for extra hardware arrrangements such as an interface, output buffer, connector, etc. for transmitting the measured data stored in the memory. Thus, the prior art suffers from the disadvantages that the overall size of the electronic sphygmomanometer increases and the cost of the instrument rises.